RSU as a collateral

Can I use my RSU as a collateral to buy a house before the vested date?

Seems unlikely. To be sure you have to ask the mortgage bank directly. Regarding collaterals, Swiss banks may have different policies.

Swiss banks generally only accept collateral that is deposited with them (their own bank accounts, stock funds, etc.). Banks also generally only offer Lombard loans for actual shares, and not for vested shares, stock options, etc. So I doubt you could use RSUs as collateral. But it certainly doesn't hurt to ask your custodian bank if there is any solution.